3  EPA Ecoregions

For some geological classification that isn’t based on watershed boundaries, we turn to the EPA’s Ecoregions.

Intent here is to list which ecoregions are in our watershed, and which are in each basin (using MDEQ’s divisions). And maybe how much are of each basin belongs to each ecoregion. Plus show a map.

3.0.1 Level 3 Ecoregions

Figure 3.1: Level 3 Ecoregions in Louisiana, Mississippi, and Alabama; the Mississippi Sound Watershed is outlined in black.

The Mississippi Sound Watershed contains 4 level-3 ecoregions:

• 65 Southeastern Plains
  
• 73 Mississippi Alluvial Plain (in the very southwest corner)
  
• 74 Mississippi Valley Loess Plains
  
• 75 Southern Coastal Plain

Figure 3.2: Level 3 Ecoregions in the Mississippi Sound Watershed only.

3.0.2 Level 4 Ecoregions

Figure 3.3: Level 4 Ecoregions in the Mississippi Sound Watershed.

3.1 Data Sources

The .qmd file that generated this section was: EPA_Ecoregions.qmd.

3.1.0.1 Ecoregions

Level 3 and 4 Ecoregion shapefiles were downloaded from the EPA’s website on 16 June 2025 for the states of MS, AL, and LA.

The original downloaded files along with their metadata files are available in the EPA EcoRegions folder of the msepCharacterization data files directory.

Those files were read in, combined, and clipped to the Mississippi Sound Watershed boundaries (using the outline_full object from the {msepBoundaries} package) using the script EPAEcoRegion_subsetting.R (on github) in the R_preprocessing folder. Three objects resulted: level3_lamsal, level 3 ecoregions for the 3 states combined; level3_mssoundwatershed, level 3 ecoregions trimmed to only the Mississippi Sound Watershed area; and level4_mssoundwatershed, level 4 ecoregions trimmed to only the Mississippi Sound Watershed area. The level 4 ecoregions for the entire three states were not retained because there were so many categories; it really only makes sense to look at these at the smaller level.

The resulting objects were saved as layers of a geopackage, EPA_EcoRegion.gpkg in the data/processed folder. These files are available in the processed folder of the msepCharacterization data files directory.